It is known to make electrical laminates and other composites from a fibrous reinforcement and an organic matrix resin such as an epoxy-containing matrix. Examples of suitable processes usually contain the following steps:
(1) An epoxy-containing formulation is applied to, or impregnated into, a substrate by rolling, dipping, spraying, other known techniques and/or combinations thereof. The substrate is typically a woven or nonwoven fiber mat containing, for instance, glass fibers or paper.
(2) The impregnated substrate is “B-staged” by heating at a temperature sufficient to draw off solvent in the epoxy formulation and optionally to partially cure the epoxy formulation, so that the impregnated substrate can be handled easily. The “B-staging” step is usually carried out at a temperature of from 90° C. to 210° C. and for a time of from 1 minute to 15 minutes. The impregnated substrate that results from B-staging is called a “prepreg.” The temperature is most commonly 100° C. for composites and 130° C. to 200° C. for electrical laminates.
(3) One or more sheets of prepreg are stacked or laid up in alternating layers with one or more sheets of a conductive material, such as copper foil, if an electrical laminate is desired.
(4) The laid-up sheets are pressed at high temperature and pressure for a time sufficient to cure the resin and form a laminate. The temperature of this lamination step is usually between 100° C. and 230° C., and is most often between 165° C. and 190° C. The lamination step may also be carried out in two or more stages, such as a first stage between 100° C. and 150° C. and a second stage at between 165° C. and 190° C. The pressure is usually between 50 N/cm2 and 500 N/cm2. The lamination step is usually carried out for a time of from 1 minute to 200 minutes, and most often for 45 minutes to 90 minutes. The lamination step may optionally be carried out at higher temperatures for shorter times (such as in continuous lamination processes) or for longer times at lower temperatures (such as in low energy press processes).
Optionally, the resulting laminate, for example, a copper-clad laminate, may be post-treated by heating for a time at high temperature and ambient pressure. The temperature of post-treatment is usually between 120° C. and 250° C. The post-treatment time usually is between 30 minutes and 12 hours.
The current trend of the electrical laminates industry requires materials with improved dielectric properties including lower dielectric constant (Dk) and loss factor (Df); superior thermal properties including high glass transition temperature (Tg) and decomposition temperature (Td); and good processability.
Heretofore, various methods have been used to try to improve the dielectric constant of electrical laminates made from epoxy-containing resin compositions including, for example, by adding various thermoplastic additives, such as polyphenylene oxide (PPO), polyphenylene ether (PPE), or allylated polyphenylene ether (APPE), to the epoxy-containing resin composition.
It is desired to provide a new pathway to reduce the dielectric constant of electrical laminates made from organic resins. More particularly, it is desired to prepare modified organic resins, such as epoxy-containing resins, with thermolabile groups to lead to nanoporous matrixes upon curing.